One of the strategies employed to improve the ethanolic fermentation is the utilization
of immobilized cells. Cell immobilization consists of the attachment of
cells into a support or a location in a defined space in order to utilize, in a controlled
way, their capacity to accomplish biological transformation. Thus, the cells
do not leave the bioreactor, and continuous fermentation processes can be implemented.
In this case, the substrates contained in the feed stream are transformed
into products in the biocatalyst (cells + support) bed. These products abandon the
system in the cell-free effluent stream. This leads to an easier product recovery as
well as avoiding the risk of cell washout. A better control of the fermentation process
is achieved compared to suspended cell cultivation for which microbial cells
are continuously removed from the fermenter. On the other hand, the biocatalyst
can be readily recovered if the process is carried out in batch regime. All of these
advantages make reactors with immobilized cells exhibit higher productivities
allowing the utilization of smaller bioreactors (lower capital costs).